[PATCH v3] idle/x86: remove the call to boot_init_stack_canary() from cpu_startup_entry()

[Christophe Leroy]

commit d7880812b359 ("idle: Add the stack canary init to
cpu_startup_entry()") added the call to boot_init_stack_canary()
in cpu_startup_entry() in an #ifdef CONFIG_X86 statement, with
the intention to remove that #ifdef later.

While implementing stack protector for powerpc, it has been
observed that calling boot_init_stack_canary() is also needed
for powerpc which uses per task (TLS) stack canary like the X86.

However, calling boot_init_stack_canary() would break arches
using global stack canary (ARM, SH, MIPS and XTENSA).

Instead of modifying the #ifdef CONFIG_X86 in an
 #if defined(CONFIG_X86) || defined(CONFIG_PPC), powerpc
implemented the call to boot_init_stack_canary() in the function
calling cpu_startup_entry()

On x86, we have two functions calling cpu_startup_entry():
- start_secondary()
- cpu_bringup_and_idle()

start_secondary() already calls boot_init_stack_canary().

This patch adds the call to boot_init_stack_canary() in
cpu_bringup_and_idle() and removes it from cpu_startup_entry()

Reviewed-by: Juergen Gross <jgross@xxxxxxxx>
Signed-off-by: Christophe Leroy <christophe.leroy@xxxxxx>
---
 v3: Fixed linux/stackprotector.h inclusion

 v2: Revised commit log (#if defined  had been droped by 'git commit')

 arch/x86/xen/smp_pv.c |  2 ++
 kernel/sched/idle.c   | 15 ---------------
 kernel/sched/sched.h  |  1 -
 3 files changed, 2 insertions(+), 16 deletions(-)

diff --git a/arch/x86/xen/smp_pv.c b/arch/x86/xen/smp_pv.c
index e3b18ad49889..145506f9fdbe 100644
--- a/arch/x86/xen/smp_pv.c
+++ b/arch/x86/xen/smp_pv.c
@@ -22,6 +22,7 @@
 #include <linux/tick.h>
 #include <linux/nmi.h>
 #include <linux/cpuhotplug.h>
+#include <linux/stackprotector.h>
 
 #include <asm/paravirt.h>
 #include <asm/desc.h>
@@ -88,6 +89,7 @@ static void cpu_bringup(void)
 asmlinkage __visible void cpu_bringup_and_idle(void)
 {
 	cpu_bringup();
+	boot_init_stack_canary();
 	cpu_startup_entry(CPUHP_AP_ONLINE_IDLE);
 }
 
diff --git a/kernel/sched/idle.c b/kernel/sched/idle.c
index 16f84142f2f4..f5516bae0c1b 100644
--- a/kernel/sched/idle.c
+++ b/kernel/sched/idle.c
@@ -347,21 +347,6 @@ EXPORT_SYMBOL_GPL(play_idle);
 
 void cpu_startup_entry(enum cpuhp_state state)
 {
-	/*
-	 * This #ifdef needs to die, but it's too late in the cycle to
-	 * make this generic (ARM and SH have never invoked the canary
-	 * init for the non boot CPUs!). Will be fixed in 3.11
-	 */
-#ifdef CONFIG_X86
-	/*
-	 * If we're the non-boot CPU, nothing set the stack canary up
-	 * for us. The boot CPU already has it initialized but no harm
-	 * in doing it again. This is a good place for updating it, as
-	 * we wont ever return from this function (so the invalid
-	 * canaries already on the stack wont ever trigger).
-	 */
-	boot_init_stack_canary();
-#endif
 	arch_cpu_idle_prepare();
 	cpuhp_online_idle(state);
 	while (1)
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 455fa330de04..75a718ef771d 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -56,7 +56,6 @@
 #include <linux/profile.h>
 #include <linux/rcupdate_wait.h>
 #include <linux/security.h>
-#include <linux/stackprotector.h>
 #include <linux/stop_machine.h>
 #include <linux/suspend.h>
 #include <linux/swait.h>
-- 
2.17.1